As a result of improvement in recent years in display apparatus in terms of the resolution and in performance of image pickup apparatus such as a digital video camera, such piracy that a literary work such as a cinema or a video image displayed on a display apparatus such as a screen or a display unit is picked up directly as an image and distributed illegally has become a serious problem. It is forecast estimated, as such improvement in display apparatus and image pickup apparatus further proceeds in future, the situation becomes further serious.
It is to be noted that, in the present specification, an action of picking up an image on a display apparatus illegally by means of a video camera or the like is referred to as “(image) re-pickup”.
In order to deal with such image re-pickup, such a technique for preventing the image re-pickup as to provide distortion only on a re-picked up image picked up by a video camera or the like without allowing a spectator who observes an image to recognize the distortion has been laid open.
For example, U.S. Pat. No. 5,680,454 discloses a technique wherein the frame rate of a display apparatus is varied with respect to time in accordance with a pseudo-random noise sequence. This makes an image pickup person to establish frame rate synchronism, and as a result, distortion is provided on a re-picked up image.
U.S. Pat. No. 6,018,374 discloses a technique wherein a message is projected using infrared rays in an overlapping relationship with an image on a screen to place the message into a re-picked up image of a CCD video camera which is sensible to infrared rays to disorder the re-picked up image.
Japanese Patent Laid-Open No. 2002-314938 discloses a technique wherein a pixel display is turned on and off (intensity modulated) at a rate at which the human being cannot recognize to display a symbol, a random pattern or characters on a re-picked up image.
Japanese Patent Laid-Open No. 2002-519724 discloses a technique wherein the frame rate, line rate or pixel rate is varied frequently in accordance with an unpredictable sequence created by a cryptographically safe algorithm or a natural source, or the frame rate is varied in accordance with the variation amount of a scene to provide distortion on a re-picked up image.
In the meantime, also a great number of techniques for placing an electronic watermark into an image have been developed. As an electronic watermark to be placed in an image, usually an “invisible watermark” which cannot be visually recognized by the audience is used. The invisible watermark can be used to embed information, for example, of the title of the image, a serial number unique to the image, the name of a producing person, the name of a distributor and so forth into an image. A person or an organization that has the copyright would claim the copyright of a re-picked up image based on the embedded information.
The prior art techniques described above except the electronic watermark are all intended to disorder a re-picked up image.
Actually, however, it is not impossible to perform image re-pickup such that the image is not disordered or no message is included.
For example, in order to cope with the technique of U.S. Pat. No. 6,018,374, only if an optical filter for removing infrared rays is placed in front of a video camera, the effect of the technique can be eliminated simply by anyone.
Also as regards the techniques disclosed in the other patent documents mentioned hereinabove, if a video camera whose shutter speed or frame rate can be adjusted optimally is used, then the distortion which may appear on a re-picked up image can be moderated although it is difficult to completely remove the distortion of the image.
From the foregoing, the method of disordering a re-picked up image to prevent distribution of an illegal re-picked up image is limited in the suppression effect.
On the other hand, as regards the techniques which use an electronic watermark, since they use an invisible watermark, that is, since they are not directed to disordering of an image, a person who observes the re-picked up image cannot visually distinguish whether the image is a re-picked up image illegally picked up or an image which is not illegal. Therefore, the effect of suppressing the distribution of a re-picked up image by disordering the image itself cannot be anticipated. The techniques suppress re-image pickup indirectly by giving a warning or enabling claiming of the right to a person who executes re-pickup of an image/distributes a re-picked up image.
However, an action of placing an electronic watermark into an image corresponds in a certain sense to disordering of an original image to degrade the picture quality. Therefore, to an author or an image producing person who attaches importance to the picture quality of an image, the action itself corresponds to modification to the literary work, and the author or image producing person may show disapproval of use of an electronic watermark. Therefore, there is a situation wherein the technique itself cannot be executed readily.